Magnetic head

ABSTRACT

The present invention provides a magnetic head of which magnetic core is composed of thin plates of a high magnetic permeability, each provided with an adhesive layer comprising a granular substance. In such structure, the stress relaxation achieved by said granular substance prevents the loss of effective magnetic permeability of said core, thereby improving the high frequency characteristics. Also the presence of said granular substance realizes a hardness in the vicinity of said adhesive higher than that of said thin plates of a high magnetic permeability, thereby improving the abrasion resistance of said core. Furthermore said adhesive layer is rendered satisfactorily thinner than said thin plate to prevent the loss of sensitivity. Furthermore a fixing member for supporting said core is made of such a composition as to be evenly abraded with said core, thereby preventing deformation of the head resulting from abrasion by the recording medium and thus enabling to maintain the initial electromagnetic converting characteristics over a prolonged period.

This is a continuation, of application Ser. No. 230,107, filed Jan. 29,1981, now U.S. Pat. No. 4,368,496 which was a continuation ofapplication Ser. No. 14,849, filed Feb. 26, 1979, abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic head improved in theelectromagnetic converting characteristics and abrasion resistance byproviding thin plates of a high magnetic permeability with an adhesivelayer comprising a granular substance.

2. Description of the Prior Art

The magnetic head, being designed for information recording and playbackby friction contact with a magnetic tape, is gradually abraded at itscontact surface with the magnetic tape to lose the recording performancein the higher frequency region in the beginning and to eventually resultin a deterioration of the recording performance over the entirefrequency range as the abrasion proceeds. Such drawback can be preventedby increasing the abrasion resistance to reduce the amount of abrasionand to cause the abrasion to occur in a uniform manner. For example incase of an audio cassette tape recorder with a recording track width ofca. 0.6 mm, the stereo magnetic head is composed of four laminated thinplates each 0.15 mm thick to obtain the above-mentioned track width,since a single plate of a 0.6 mm thickness will result in a significanteddy current loss, leading to a loss in the electromagnetic convertingefficiency. In such structure said laminated thin plates have to bemutually insulated electrically, and are therefore composed of amaterial of a high magnetic permeability such as permalloy or sendusteach provided on the surfaces thereof with a resinous insulatingadhesive. Consequently the track face of the magnetic head is composedof an alternating laminated structure of said material of high magneticpermeability and said adhesive layer. Such laminated structure isgenerally obtained by forming a thin layer for example of an epoxyresin, for example by spraying, on thin plates of a high magneticpermeability and compressing such plates under heating. In suchstructure, however, said resin layer tends to generate a stress alongthe surface of said thin plates at the hardening of resin afterlamination, thus resulting in a deterioration of magnetic properties. Onthe other hand a resin with a low stress generation generally providesan excessively low adhesive force. In the conventional magnetic headssaid material of high magnetic permeability has been changed frompermalloy to less-abradable materials such as hard permalloy or sendustwhile said adhesive has been of a lower abrasion resistance than that ofsaid material of high magnetic permeability in order to ensure asatisfactory adhesion, but it is to be noted that the abrasionresistance of the entire magnetic core is also affected by the abrasionresistance of said adhesive. Furthermore said magnetic core, after coilwinding, is inserted into a head case and fixed therein by means of afixing material to be filled between said core and said case, so that apart of said fixing material will constitute, together with saidmagnetic core, the contact face with the magnetic tape. It is thereforenecessary, in order to maintain the initial performance of the head fora prolonged period, that said core and said fixing material are evenlyabraded to always maintain a flat contact face. In the conventionalmagnetic heads, however, the service life has been inevitably limiteddue to unbalanced abrasion of the head core and the fixing material.

SUMMARY OF THE INVENTION

A first object of the present invention is to provide a magnetic head ofimproved high frequency characteristics through relaxation of stressgenerated at the hardening of the adhesive thereby preventing the lossin the effective magnetic permeability of the core.

A second object of the present invention is to provide a magnetic headwith an improved abrasion resistance of the core by rendering saidadhesive harder than the thin plates of a high magnetic permeabilityconstituting the core.

A third object of the present invention is to provide a magnetic headwherein the sensitivity loss resulting from the presence of saidadhesive is reduced.

A fourth object of the present invention is to provide a magnetic headwherein the core and the fixing material present therearound are evenlyabraded to ensure stable electromagnetic converting performance over aprolonged period.

A fifth object of the present invention is to provide a magnetic head ofa prolonged service life.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a head element adapted for use in thepresent invention and formed by winding coil on a core;

FIG. 2 is a perspective view of the head element shown in FIG. 1 placedin a head casing;

FIG. 3 is a cross-sectional view of the magnetic head of the presentinvention in a state in contact with a magnetic tape and a tape pad;

FIG. 4 is a chart of effective permeability-frequency relationship in acomparison of the head of the present invention with a conventionalmagnetic head;

FIG. 5 is a chart showing a relationship of the abraded depth of thecore vs. the tape traveling time in the comparison of the magnetic headof the present invention with that of a conventional head;

FIG. 6(a) is a partial cross-sectional view of a conventionalmulti-element magnetic head showing an abraded state thereof; and

FIG. 6(b) is a partial cross-sectional view of a multi-elementembodiment of the magnetic head of the present invention showing anabraded state thereof.

FIG. 7 is a perspective view of a head element of the present invention,similar to that shown in FIG. 1, but wherein only a single magneticallypermeable plate is provided.

FIG. 8 is a perspective view of the head element shown in FIG. 7 placedin a head casing.

FIG. 9 is a cross-sectional view of the magnetic head of FIG. 8 incontact with a magnetic tape and tape pad.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 there is shown, in a perspective view, a head core composed ofcore halves 1, 2 and provided partially thereon with a coil 3. The thinplates 1a, 1b, 1c and 1d constituting said core half 1 are respectivelycomposed of a material of a high magnetic permeability such as permalloy(hardness Hv 139) or sendust (hardness Hv 480) of a determined thicknessand are provided on the surfaces thereof with an insulating adhesivelayer of an abrasion resistance higher than that of said highpermeability material and of a thickness sufficiently smaller than theabove-mentioned determined thickness of thin plates. The core half 1formed in this manner from the laminated thin plates 1a-1d withinterleaved adhesive layers is adjoined to another core half 2 similarto said core half 1 as shown by the chain lines to form a core gap 4,whereby said core halves 1 and 2 constituting a closed magnetic circuit.

In FIG. 2 there is shown, in a partial perspective view, the magnetichead of the present invention composed of the core halves, 1, 2 and coil3 of FIG. 1 which are placed in a head case 6 and fixed therein by meansof a fixing material 7 filled into said case.

FIG. 3 is a cross-sectional view of the magnetic head in FIG. 2 alongthe chain line 5 and seen from the direction of arrow A, wherein thereare additionally shown a tape pad 8 and a magnetic tape 9. In FIG. 3 theafore-mentioned adhesive 10 is present in the spaces between said thinplates 1a-1d to mutually adhere said thin plates of a high magneticpermeability and to mutually insulate said thin plates thereby reducingthe eddy current loss therein. Said adhesive 10 is for example composedof an insulating and adhesive epoxy resin comprising a granularsubstance of a particle size in a range of 0.5 to 15 microns. Saidgranular substance is an inorganic material composed of at least amember selected from metal oxides such as SiO₂, Al₂ O₃ (hardness Hv1950), Zr(SiO₄), Al₂ O₃ --SiO₂ compounds (each of the followingcompounds is understood to include all the family compounds), Al₂ O₃--MgO (MgO hardness Hv 600), Al₂ O₃ --MgO--SiO₂, MgO--SiO₂, K₂ O--Al₂ O₃--SiO₂, Ti--O, Zr--O, Hf--O, V--O, Nb--O, Ta--O, Cr--O, Pd--O, Re--O,Mo--O, W--O, Mn--O, Fe--O, Co--O, Rh--O, Ir--O, Ni--O, Pt--O, Ti--Zr--O,Ti--Hf--O, Ti--Ta--O, Ti--Co--O, Ti--V--O, Ti--Nb--O, Ti--W--O,Ti--Mn--O, Ti--Fe--O, Zr--Hf--O, Zr--V--O, Zr--Nb--O, Zr--Ta--O,Zr--Cr--O, Zr--Mo--O, Zr--W--O, Zr--Mn--O, Zr--Re--O, Zr--Fe--O,Zr--Co--O, Zr--Ni--O, V--Nb--O, V--Ta--O, V--Cr--O, V--Mo--O, V--W--O,V--Mn--O, V--Re--O, V--Fe--O, V--Co--O, V--Ni--O, Nb--Ta--O, Nb--Cr--O,Nb--Mo--O, Nb--W--O, Nb--Mn--O, Nb--Re--O, Nb--Fe--O, Nb--Co--O,Nb--Ni--O, Ta--Cr--O, Ta--Mo--O, Ta--W--O, Ta--Mn--O, Ta--Re--O,Ta--Fe--O, Ta--Co--O, Ta--Ni--O, Cr--Mo--O, Cr--W--O, Cr--Mn--O,Cr--Re--O, Cr--Fe--O, Cr--Co--O, Cr--Ni--O, Mo--W--O, Mo--Mn--O,Mo--Fe--O, Mo--Co--O, Mo--Ni--O, W--Mn--O, W--Re--O, W--Fe--O, W--Co--O,W--Ni--O, Mn--Re--O, Mn--Co--O, Mn--Ni--O, Re--Fe--O, Re--Co--O,Re--Ni--O, Co--Ni--O etc., metal carbides such as Ti--C (hardness Hv3000), Zr--C, Hf--C, V--C, Nb--C, Ta--C, Cr--C, Mo--C, W--C, Mn--C,Fe--C, Fe--W--C, Fe--Mo--C, Co--Fe--C, Co--Mo--C, Ni--W--C, V--Zr--C,Cr--Nb--C, Mn--Mo--C, Mn--W--C, Ni--Mo--C etc., metal nitrides such asTi--N, Zr-- N, V--N, Nb--N, Ta--N, Cr--N, Mo--N, W--N, Mn--N, Fe--N,Co--N, Ti--Zr--N, Ti--Hf--N, Ti--V--N, Ti--Nb--N, Ti--Ta--N, Ti--Co--N,Ti--Ni--N, Zr--Nb--N, V--Nb--N, V--Ta--N, Ta--Cr--N, Ta--Mn--N,Ta--Fe--N, Ta--Co--N, Ta--Ni--N, Cr--Mo--N, Cr--Mn--N, Cr--Fe--N,Mo--(Mn, Fe, Co, Ni)--N, Mo--Co--N, Mo--Ni--N, Mn--Fe--N, Fe--Ni--N,Fe--Pd--N etc., metal borides such as Ti--B, Zr--B, Hf--B, V--B, Nb--B,Ta--B, Cr--B, Mo--B, W--B, Mn--B, Ni--B, Pd--B, Ti--Zr--B, Ti--Hf--B,Zr--Hf--B, Ti--V--B, Ti--Nb--B, Ti--Ta--B, Ti--Cr--B, Ti--Mo--B,Zr--Nb--B, Zr--Ta--B, Zr--Mo--B, V--Cr--B, Nb--Cr--B, Ta--Cr--B,Ta--Fe--B, Ta--Co--B, Ta--Ni--B, Cr--Mo--B, Cr--Mn--B, Cr--Fe--B,Cr--Co--B, Cr--Ni--B, Mo--Fe--B, Mo--Co--B, Mo--Ni--B, Mn--Fe-- B,Mn--Co--B, Mn--Ni--B, Fe--Co--B, Mo--Al--B, Co--Al--B, Ni--Al--B,Co--Mg--B, Ni--Mg--B, Co--Zn--B, Ni--Zn--B, Co--Ga--B, Ni--Ga--B,Co--Ge--B, Ni--Ge--B, Co--Sn--B, Ni--Sn--B, Co--In--B, Ni--In--B etc.,and metal silicides such as T--Si (hardness Hv 700), Zr--Si, Hf--Si,V--Si, Nb--Si, Ta--Si, Cr--Si, Mo--Si, W--Si, Mn--Si, Fe--Si, Co--Si,Rh--Si, Ir--Si, Ni--Si, Pb--Si, Pt--Si, Ti--Zr--Si, Ti--Hf--Si,Ti--V--Si, Ti--Ta--Si, Ti--Cr--Si, Ti--Mo--Si, Ti--W--Si, Ti--Ni--Si,Ti--Mn--Si, Ti--Re--Si, Zr--V--Si, Zr--Nb--Si, Zr--Ta--Si, Zr--Mo--Si,Zr--W--Si, Hf--W--Si, Zr--Co--Si, Zr--Ni--Si, Hf--Ni--Si, Zr--Fe--Si,Hf--Fe--Si, V--Nb--Si, V--Mo--Si, V--Mn--Si, V--Fe--Si, V--Co--Si,V--Ni--Si, Nb--Gr--Si, Ta--Cr--Si, Ta--Mo--Si, Nb--W--Si, Ta--W--Si,Nb--Fe--Si, Nb--Co--Si, Ta--Co--Si, Nb--Ni--Si, Ta--Ni--Si, Nb--Mo--Si,Cr--Mo--Si, Cr--W--Si, Cr--Mn--Si, Cr--Fe--Si, Cr--Co--Si, Cr--Ni--Si,Mo--W--Si, W--Mn--Si, Mo--Fe--Si, Mo--Fe--Si, W--Fe--Si, Mo--Co--Si,W--Co--Si, Mo--Ni--Si, W--Ni--Si etc. The amount of such inorganicgranular substance should at least equal to 20% for achieving asatisfactory effect, but at the same time should not exceed 70% in orderto avoid deterioration of the adhesion to the thin plates and also toprevent inefficient coating work at a high viscosity. Consequently thepreferred range of the amount of said inorganic granular substance isfrom 20 to 70%.

The inorganic granular substance of a particle size in excess of 15microns will excessively enlarge the spacing between the thin plates andthus will deteriorate the sensitivity of the magnetic head since theeffective thickness of the magnetic layer on the tape contact face isreduced for a given track width. Also the presence of such largegranules will locally reduce the amount of resinous binder, therebyreducing the adhering force thereof.

On the other hand the granules of a size smaller than 0.5 microns canonly be mixed in a limited amount with the epoxy resin due tosignificant increase in the viscosity and are therefore unable toperform sufficient stress relaxation. Also a minimum particle diameterof 0.5 microns is required in order to prevent mutual contact of thehigh permeability thin plates which generally show surface irregularityin the order of ±0.2 microns. Consequently the preferred range for theparticle size of said inorganic granular substance is from 0.5 to 15microns. In this manner the above-explained adhesive layer employed inthe magnetic head of the present invention shows satisfactory electricinsulation, abrasion resistance, coating efficiency, adhering force andstress relaxation, wherein said stress relaxation functions to preventthe eventual deformation of core at the hardening of the resinousbinder, thereby preventing the loss in the effective magneticpermeability.

FIG. 4 shows the plotting of effective permeability in ordinate againstfrequency in abscissa, wherein the curve 11 shows the results ofmeasurements on a conventional ring-shaped core sample laminated with anepoxy resin alone while the curve 12 shows those of a ring-shaped coresample laminated with an epoxy resin containing powdered alumina (Al₂O₃) of an average particle size of 1 micron in an amount of 30% byweight. It will be observed that the curve 12 shows a higherpermeability in the entire frequency range of 0.3-100 KHz, particularlyat the high frequency region. Also the smaller separation between thecurves 12a and 12b than between the curves 11a and 11b indicates thesmaller fluctuation of characteristics between multiple core samples.This result will be ascribable to a fact that the granular substance ofa large surface area absorbs a considerable portion of the stressgenerated by the contraction of the resin, thereby relaxing the stressappearing on the core surface. Also said granular substance prevents themutual contact between the adjacent thin plates, thereby reducing theeddy current loss therein and preventing the deterioration of the highfrequency characteristics. In the absence of such granular substance,the eventual surface irregularities present on said thin plates tend tocause mutual contact of said thin plates through pinholes or unevenspots of the adhesive layer. In this manner the magnetic head of thepresent invention utilizing the laminated thin plates added with saidinorganic granular substance is provided with an improved sensitivity inthe high frequency region and with a reduced high frequency biascurrent. Also by rendering the thickness of said adhesive 10 (dimensionin the lateral direction in FIG. 3) satisfactorily smaller than thethickness of said thin plate (dimension in the lateral direction in FIG.3), the contact area between the high permeability material and themagnetic tape can be increased to avoid the loss of sensitivity.

FIG. 5 shows the abrasion depth of magnetic core as a function of taperunning time at a tape speed of 4.75 cm/sec. wherein the line 13,representing a first example of the present invention with a track widthof ca. 0.6 mm prepared by laminating six hard permalloy plates each 0.1mm thick and respectively coated with an adhesive in a thickness of0.001 mm having a higher hardness and a higher abrasion resistance thansaid hard permalloy, shows abrasion depth of 8 microns at a running timeof 300 hours, while the line 15 representing an identical example exceptfor utilizing another adhesive of a lower abrasion resistance shows anabrasion depth of 48 microns after a running time of 300 hours. Also asecond example of the magnetic head of the present invention with atrack width of ca. 0.6 mm, prepared by laminating two high permeabilitysendust thin plate each 0.3 mm thick and respectively coated with anadhesive in a thickness of 0.01 mm having a higher hardness and a higherabrasion resistance than said sendust, shows an abrasion depth of 6microns after a running time of 300 hours as shown by the line 14, whilean identical head except for employing an adhesive of an abrasionresistance lower than that of said sendust shows an abrasion depth of 18microns after a running time of 300 hours as shown by the line 16. Alsothe heads of the first and second examples of the present invention showalmost no change in the electromagnetic converting characteristicsbefore and after the running test.

Although the foregoing examples utilize plural laminated thin plates, itis also possible to improve the abrasion resistance even when a singleplate of high magnetic permeability is employed if said plate is coatedon both sides thereof with an adhesive material of a high abrasionresistance. For example, the core is of a non-laminated structure for amagnetic head with a track width of 0.1-0.03 mm such as a videorecording head, but also in such case the abrasion of the core can bereduced by coating an adhesive as aforementioned on both sides of thecore plate. Thus, as explained in the foregoing, it is rendered possibleto realize a magnetic head with an extended service life withoutdeteriorating the electromagnetic converting characteristics byselecting the abrasion resistance of said adhesive higher than that ofthe said high permeability thin plates and also selecting the thicknessof said adhesive satisfactorily smaller than that of said thin plates.

In this regard, reference is made to FIGS. 7, 8 and 9, showing a singleplate embodiment of the invention, wherein the same reference numeralsare used to refer to elements corresponding to those shown in FIGS. 1, 2and 3.

FIGS. 6a and 6b are cross-sectional views of the magnetic head of FIG. 2along the chain line 5 and seen from the direction of arrow A, whereinsaid head is constructed with four channels, and c and d representingthe boundaries of the contact area with the magnetic tape. FIG. 6aillustrates the cross section of a conventional multichannel magnetichead as a reference, wherein the chain line 17a and the full line 17brespectively indicate the tape contact surfaces before and after theabrasion test, while FIG. 6b illustrates the cross section of themagnetic head of the present invention, wherein the line 18a and thefull line 18b respectively indicate the tape contact surfaces before andafter the abrasion test. In FIGS. 6a and 6b the abrasion is caused by arunning test for 200 hours with an unrepresented magnetic tape with atape speed of 4.75 cm/sec, and the vertical dimension is enlarged 100times with respect to the horizontal dimension in order to clarify thestate of abrasion. From the comparison of these two drawings it will beapparent that the magnetic head of the present invention, shown in FIG.6b has a superior abrasion resistance. In this third example of thepresent invention shown therein, the adhesive 10a is provided in thespacings between the laminated thin plates 1a-1d to electricallyinsulate the adjacent thin plates of a high permeability therebyreducing the eddy current loss therein and also to improve the abrasionresistance. Said adhesive 10a is composed of an epoxy resin added withan inorganic granular substance consisting of at least a member selectedfrom the aforementioned metal oxides, metal carbides, metal nitrides,metal borides, and metal silicides. Said inorganic granular substance ispreferably added in an amount within a range from 20 to 70% as alreadyexplained in connection with FIG. 3, and is most preferably composed ofalumina.

The fixing material 7a is composed of an epoxy resin added with SiO₂(silica) in an amount of 20-50 wt. % or Al₂ O₃ (alumina) in an amount of1-5 wt. %. Further CaCO₃ (calcium carbonate) is added in such a mannerthat the total amount of the above-mentioned additives represents 30-80wt. % of the mixture, in order to prevent time-dependent deterioratingand to relax the stress caused by the contraction at the hardening.

The magnetic head of the present invention prepared with the adhesiveand the fixing material of the above-explained compositions is providedwith an elevated abrasion resistance at the tape contact surface and isabraded evenly on said surface as shown in FIG. 6b. Consequently it isrendered possible to maintain satisfactory magnetic characteristics overa prolonged period and thus to achieve an extended service life.

What we claim is:
 1. A magnetic head, comprising:a head core including aplurality of core halves joined to each other, each of said core halvescomprising at least one thin plate of predetermined thickness composedof a high-magnetic permeability material and at least two adhesivelayers adhered to and solidified on opposing surfaces of said plate,said adhesive layers being composed of an electrically insulative resinand fine inorganic granular particles of a material harder than saidhigh magnetic permeability material, said particles being added to saidresin in an amount of from 20 to 70 percent by weight of said resin suchthat said adhesive layers have a higher degree of abrasion resistancethan said plate, the thickness of said adhesive layers being in a rangeof from one-hundredth to one-thirtieth said predetermined thickness ofsaid plate; a coil wound on said head core; a case enclosing said headcore and coil; and a fixing material for enclosing said head core andsaid coil within said case, said fixing material comprising a secondresin mixed and solidified with a powder chosen from the groupconsisting of powdered SiO₂ and powdered alumina and said fixingmaterial having a degree of hardness intermediate the relatively lowdegree of hardness of said high-magnetic permeability material and therelatively high degree of hardness of said adhesive layers, such thatthe hardness of the fixing material approximates the average hardness ofthe plate and adhesive layers in composite and such that said plate,said adhesive layers and said fixing material all abrade at asubstantially uniform rate, whereby degradation of performance due touneven abrasion of said plate, said layers, and said fixing material ismitigated.
 2. The magnetic head of claim 27, wherein there are provideda plurality of said thin plates of high-magnetic permeability materialand wherein said adhesive layers are interleaved therebetween.
 3. Amagnetic head in accordance with claims 1 or 2, wherein saidelectrically insulative resin comprises an epoxy resin, and said fineinorganic particles comprise fine alumina particles which are added tosaid epoxy resin in said amount of from 20 to 70 percent by weight ofsaid epoxy resin, and wherein said second resin comprises a second epoxyresin to which said powdered SiO₂ is added in an amount of from 20 to 50percent by weight of said second epoxy resin.
 4. A magnetic head inaccordance with claim 3, wherein said second epoxy resin furtherincludes powdered CaCO₃ in such an amount that said powdered SiO₂ andCaCO₃ are present, in total, in said second epoxy resin in an amount offrom 30 to 80 percent by weight of said second epoxy resin.
 5. Amagnetic head in accordance with claims 1 or 2, wherein saidelectrically insulative resin comprises an epoxy resin, and said fineinorganic particles comprise fine alumina particles which are added tosaid epoxy resin in said amount of from 20 to 70 percent by weight ofsaid epoxy resin, and wherein said second resin comprises a second epoxyresin to which said powdered alumina is added in an amount of from 1 to15 percent by weight of said second epoxy resin.
 6. A magnetic head inaccordance with claim 5, wherein said second epoxy resin furtherincludes powdered CaCO₃ in such an amount that said powdered alumina andCaCO₃ are present, in total, in said second epoxy resin in an amount offrom 30 to 80 percent by weight of said second epoxy resin.